Vaccine halves cancer-causing HPV infections in US teen girls

It’s welcome news. Vaccination against human papilloma virus has more than halved the number of HPV infections in the US – the leading cause of cervical cancer – despite its relatively low uptake in the country.

The growing body of evidence that HPV vaccination works may convince more countries to give the vaccine to teenage boys, as HPV also causes cancers of the mouth, throat and anus, as well as genital warts.

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“It supports the case to strive for as much coverage as possible,” says Johannes Bogaards of the National Institute for Public Health and the Environment at Bilthoven in the Netherlands, who wasn’t involved in the latest study.

Almost everyone who has sex without a condom will catch HPV at some point; the virus dwells in the moist mucosal tissues of the genitals and mouth and can be passed on via semen and vaginal fluids. Most people shake off the infection, but in some it lingers, causing cervical cancer after about 20 years.

As large-scale vaccination only started a decade ago, it’s too soon to see any fall in cervical cancer rates – although studies have shown that cases of genital warts, which occur within months of HPV infection, are already falling. For instance, in Australia, one of the first countries to introduce the vaccine, cases of genital warts have decreased by 61 per cent.

Vocal opponents

Nevertheless, the HPV vaccine has some vocal opponents. As well as anti-vaccine sentiments, there are also those who say it could encourage teens to have unprotected sex.

The new study looked at data collected through large health surveys performed regularly in the US, which included a brief medical check-up. Researchers combined results from the latest two, carried out between 2009 and 2012, and found that about a third of 14 to 19-year-old girls had received all three doses of the vaccine.

These results were compared with two earlier surveys performed between 2003 and 2006, before the vaccine came in. They found that since the vaccine was introduced the number of 14 to 19-year-olds who had HPV in their vaginal fluid fell from 11.5 per cent to 4.3 per cent.

“Showing the effectiveness of a vaccination programme may help to convince doubters,” says Bogaards. He thinks that while there will always be some hard-core “anti-vaxxers”, there is a larger group of people who are more open to argument.

The study may even assuage fears the vaccine will encourage risky sexual behaviour, says Simon Barton at Imperial College London. In the later surveys, about two-thirds of vaccinated women reported having had three or more sexual partners – about the same number as the unvaccinated group.

Gardasil is available for boys in the US and Australia, but not in the UK or the Netherlands. One idea is to offer the vaccine only to gay men, as they have higher rates of anal cancer.

The case for vaccinating to prevent oral cancer isn’t as strong since mouth cancers can have other causes, such as smoking, says Bogaards. But the proportion of oral cancers caused by HPV seem to be on the rise. That could be because oral sex is becoming more common, although lower rates of smoking may also be playing a part.